This invention relates generally to refractory cement and relates more particularly to a new and improved refractory cement composition.
The refractory cement with which this invention is concerned is intended to be used as a joint compound in masonry structures expected to be exposed to high temperatures. Examples of such masonry structures include chimneys and fireplaces in which high temperature materials, such as clay flue liners or firebrick, are sealed or bonded together with the refractory cement. Refractory cements characteristically possess a high resistance to heat and, accordingly, are commonly referred to as high temperature cements.
A type of cement with which this invention is not to be compared is commonly referred to as a castable or insulating castable, such as is described in U.S. Pat. No. 3,718,489. While, on one hand, castables are comprised of ingredients having a course mesh aggregate size, refractory cements, on the other hand, are comprised of ingredients ground to a fine consistency so as to provide compositions of ingredients with a fine mesh aggregate size. Furthermore, insulating castables possess insulating characteristics due primarily to the utilization of expanded clay in the manufacture of the castable, and both castables and insulating castables may be used as a high temperature concrete to cast objects of a predetermined shape or to cast a hearth or wall section, for example, of a furnace. In contrast, refractory cements do not include expanded clay nor are intended to insulate and are used primarily as high temperature cements used to seal or bond high temperature masonry materials such as firebrick and clay flue liners.
Inasmuch as there exists conventional refractory cements for bonding or sealing high temperature masonry materials together, conventional refractory cements possess limitations. One such limitation is directed to the fact that such conventional cements are water soluble when in a cured, or hardened, condition. The exposure of these water soluble cements, when in a cured condition, to water such as may result from rainwater or a condensation of combustion products flowing down a chimney or flue tends to soften, and thus weaken, a masonry joint formed with the refractory cement. A sufficient softening of the joint, such as may result from prolonged exposure to moisture, may cause the cement to flow out of the joint.
Another limitation associated with conventional refractory cements relates to the workability of the conventional cements. More specifically, such refractory cements are commonly adapted to dry or cure in a relatively short amount of time requiring that the cement, once mixed with water, be worked relatively quickly. Some conventional refractory cements are further limited in that they require heat to harden properly or are not acid resistant in service. Inasmuch as creosote is known to contain acid, exposure of such a conventional refractory cement to creosote can have undesirable effects on the structural stability of joints comprised of the refractory cement.
Accordingly, it is an object of the present invention to provide a new and improved refractory cement which circumvents the aforediscussed limitations associated with conventional refractory cements.
Another object of the present invention is to provide such a refractory cement which is air-setting, once mixed with water.
Still another object of the present invention is to provide such a refractory cement which is non water soluble when in its hardened or cured condition.
Yet still another object of the present invention is to provide such a refractory cement which possesses a relatively high resistance to acid.
A further object of the present invention is to provide such a refractory cement which is effective in operation and economical to manufacture.